The present invention relates to shaped articles prepared from a plastically deformable composite material, to a composite material per se, to a method for rolling a plastically deformable material, and to an apparatus for rolling a plastically deformable material.
International Patent Application No. PCT/DK79/00047 discloses a particular type of material comprising a matrix, the matrix comprising densely packed particles A having a size of the order of 0.5-100 .mu.m, in particular densely packed cement particles, and inorganic solid particles B having a size of from about 50 .ANG. to about 0.5 .mu.m and being at least one order of magnitude smaller than the respective above-mentioned particles, in particular ultrafine silica particles, the smaller particles being homogeneously arranged and preferably densely packed in the voids between the larger particles.
Such materials, in the following designated DPS materials (Densified Systems containing ultrafine Particles), specifically cement-based DSP materials (that is, DSP marterials in which the particles having a size of the order of 0.5-100 .mu.m are cement particles), show a number of highly interesting properties, including high density, high tensile, bending and compressive strength, good durability, and extraordinarily good ability to anchor reinforcing bodies, including fibers, embedded in the matrix.
Due to their improved properties, cement-based DSP materials are highly desirable materials for building products, including thin-walled panels and components of the types which are nowadays often made of asbestos-reinforced cement. Due to the excellent plastic properties of the uncured DSP composite material, an attractive method for shaping such articles of DSP is a plastic deformation or compression process.
The present invention relates to important new developments connected to the preparation of shaped articles from DSP materials, in particular by plastic deformation such as extrusion, rolling, or compression.
In connection with the development of practical methods and apparatuses for the plastic deformation of the DSP materials, various new aspects of the composition and working of DSP materials have been investigated and have given rise to new developments.
One aspect of the present invention relates to compositions of cement-based DSP materials which are especially suitable for plastic deformation processes, and to shaped articles made from such compositions. Another aspect of the present invention relates to a method for rolling a DSP material or other plastically deformable material.
In the present context, the term "plastically deformable material" designates a material which, as a single phase, is deformed plastically when subjected to deformation forces such as hydrostatic pressure and displacement compulsion, including shear, as contrasted to materials which are shaped from a two-phase system such as a cement-water slurry from which liquid phase is removed during the shaping process ("slip casting"). One characteristic of cement-based DSP materials is that although they comprise cement particles and water, they show such a water retention and such an internal coherence that substantially no water will be removed from them during processing, including deformation, so that the plastic DSP paste behaves as a one phase plastically deformable material.
As disclosed in the above-mentioned International Patent Application No. PCT/DK79/00047, the particular properties of the cement-based DSP materials are ascribable to the dense packing of the cement particles with homogeneously distributed and preferably densely packed ultrafine particles in the voids between the cement particles, the dense packing of the cement particles and the simultaneous homogeneous arrangement of the ultrafine particles, in particular ultrafine silica, being obtained by a unique combination of a critical amount of water in the paste and an unconventionally high dosage of a surface-active dispersing agent, in particular a concrete superplasticizer. As surface forces which would otherwise lead to "particle locking" between the cement particles and between the ultrafine particles have been overcome by means of the high dosage of the surface-active dispersing agent, a system has been obtained in which the resistance to particle packing is solely due to particle geometry.
In the practical exploitation of cement-based DSP materials for the mass-production of shaped articles by plastic deformation, it has been found that certain problems may arise which have been solved through the principles of the present invention.
Thus, it has been found that when processing cement-based DSP materials consisting of, e.g., cement, ultrafine silica, water, concrete superplasticizer, and fibers, the processing-relevant properties of the fresh paste such as the resistance to shear deformation may vary to an undesirably high degree dependent on the time elapsed after mixing of the material. Thus, the period of time during which the material has plastic deformation properties within desirable limits may become too small for production on an industrial scale. This is the case when such a formulation is intended for extrusion. In order to possess a consistency suitable for extrusion, the formulation should have an extremely low water/dry matter ratio within narrow limits. However this extremely low water/dry matter ratio leads to serious problems in controlling the consistency of the material, and the material when shaped by plastic deformation appears with a cracky, crusty surface. Even small changes in the water/dry matter ratio of the above-mentioned basic material may give rise to serious problems:
Even a minor reduction in the water content to below a critical minimum, e.g., caused by surface evaporation, will lead to an unsaturated densely packed particle structure. The unsaturation will very soon result in solidification of the material, whereupon the material is no longer suitable for plastic deformation shaping such as low pressure extrusion, calendering or compression shaping. Throughout the present specification, "low pressure" in connection with plastic deformation shaping is intended to designate hydrostatic shaping pressures below 10 MPa.
On the other hand, even a slight excess of water compared to the critical amount results in a material which becomes sticky and is unsuitable for platic deformation extrusion as water will separate from the material into slip zones during the plastic deformation and the coherent nature of the material will be lost.